Death metal:
Mortification - Scrolls of the Megilloth
Thrash metal:
Vengeance Rising - Beheaded
Black metal:
Marduk - Voices from Avignon
Doom metal:
Paramaecium - I'm not to Blame.
Deathcore:
Carnifex - In Coalesce with Filth and Faith
Metalcore:
Machinemade God - Melancholy
Nu metal:
Mushroomhead - Sun Doesn't Rise
Folk metal:
Finntroll - Grottans Barn
Hardcore:
Throwdown - Burn
Post-hardcore:
He Is Legend - I am Hollywood
Math metal:
Meshuggah - New Millennium Cyanide Christ
Power metal:
The Lord Weird Slough Feg - Vargr Theme / Confrontation (Genetic Prophesy)
"Gimmick" metal:
Amon Amarth - Free Will Sacrifice
All time favourite metal:
Living Sacrifice - Conditional
You better believe I'm one of those people who separates my metal categories.
So many favourites I haven't mentioned though... Zao, Soul Embraced, Sinai Beach, The Showdown, Neaera, Mnemic, Malevolent Creation, Inhale Exhale, Impending Doom, Hypocrisy, Hell Within, Heaven Shall Burn, Gojira, Figure Four, The Famine, Extol, Dimmu Borgir, Dimension Zero, Demon Hunter, Darkane, Cradle of Filth, Caliban, The Black Dahlia Murder, The Berzerker, Behemoth, Becoming the Archetype, Antestor, The Amenta, The Agony Scene... All sorts of sub/sub-sub genres there.